The other thing to consider: GM syncromesh is "semi-synthetic" , if I recall. So its viscosity isn't as stable as temperatures change as a full synth. (Meaning greater efficiency hit for those who experience truly cold temperatures part of the year.)
I've got GM Synchromesh (full retail pop!
) in my car now, but am planning to go to a full synth of the same or lighter weight, soon.
Just trying to decide which, and then seeing if my choice is even available in my small city.